Directions

When you arrive, follow these: right, up, right, down, right, up, right, up and you'll see what looks like a overhead light. Go under and click. Go all the way to the left, and go under the red underpass. You'll encounter a staircase which you'll need to go down all the way then up. Once you enter the new area, go up and you'll find the entrance to the School.

Enter, then go left to the door at the bottom. Go to the middle, then up the stairs. Go left and exit through the door, then go up to the other stairs, and go up them. There should only be one door you can go through and then you'll encounter a giant sized Smile which will give you it.

Video Directions

Trivia

This is the only effect that seems to give Sabitsuki open eyes, not counting the Mono Eye and Cat effects.

May also be a reference to a manga named Dorohedoro, which has a group called the Cross Eyes. When someone joins the group, they tattoo crosses on that person's eyes.

Theories

Cross Eye imagery is present throughout the School and can only be seen in that world. The only other character to have this tattoo is the dark haired boy seen in the apartment before the school and in the classrooms itself, known as Smile. Many posters display eyes with crosses painted over them, implying that the tattoo effect may actually be crosses painted over Sabitsuki's eyes.

The Tattoo effect is the only "Open eyed" effect that doesn't display Sabitsuki's eyes as red, like "Mono Eye" and "Cat" do. (The Mono Eye, being so big, may show that it's very noticeable, and the cat may have had something to do with Sabitsuki contracting the sickness). A possible theory may be that her eyes may have been discolored or disfigured due to her sickness. In game, she always has her eyes closed (or possibly squinting). The Tattoo effect may be some sort of surgical markings or scars to correct this. She may have related to Smile because he has had similar surgeries or markings. Possibly another reason why the Kaibutsu are always laughing. This also fits in with the extreme body modification theme that is found throughout this game.